I made a simple application to add 2 numbers together but when I add two letters together or a invalid sign it crashes the program. How do I create a message box showing something saying "please put in a number" when someone inserts a letter
Here's my code:
public partial class frmAdd : Form
{
string first;
string second;
public frmAdd()
{
InitializeComponent();
}
private void btnFirst_Click(object sender, EventArgs e)
{
first = txtNumber.Text;
}
private void btnSecond_Click(object sender, EventArgs e)
{
second = txtNumber.Text;
}
private void btnResult_Click(object sender, EventArgs e)
{
int a = Convert.ToInt32(first);
int b = Convert.ToInt32(second);
int c = a + b;
txtResult.Text = c.ToString();
}
}
Use TryParse instead:
private void btnResult_Click(object sender, EventArgs e)
{
int a, b;
if (int.TryParse(first, out a) && int.TryParse(second, out b))
{
int c = a + b;
txtResult.Text = c.ToString();
}
else
{
MessageBox.Show("Invalid Input!");
}
}
Or perhaps a better method would be to trap the error when the user first inputs the data:
public partial class frmAdd : Form
{
int first; // changed to int
int second;
private void btnFirst_Click(object sender, EventArgs e)
{
if (!int.TryParse(txtNumber.Text, out this.first))
{
MessageBox.Show("Invalid Input!");
}
}
private void btnSecond_Click(object sender, EventArgs e)
{
if (!int.TryParse(txtNumber.Text, out this.second))
{
MessageBox.Show("Invalid Input!");
}
}
private void btnResult_Click(object sender, EventArgs e)
{
int c = first + second;
txtResult.Text = c.ToString();
}
}
You can use NumericUpDown control instead of TextBox - it will not allow user to input invalid data.
Or you can add validation to TextBox value after user entered something. Add ErrorProvider to your form. And subscribe to Validating event of txtNumber textbox. This event will occur when textbox loses focus. If entered text is not an integer, then error will be shown near texbox, and your button will not be clicked:
private void txtNumber_Validating(object sender, CancelEventArgs e)
{
int value;
if (!Int32.TryParse(txtNumber.Text, out value))
{
errorProvider1.SetError(txtNumber, "Value is not an integer");
return;
}
errorProvider1.SetError(txtNumber, "");
first = value; // it's better to save integer value than text
}
Validation looks like:
You can add a bit of validation to check if you can create an int from the string value passed in.
int.TryParse is a simple way of doing this.
And for the MessageBox you can just use the MessageBox calss
Example:
private void btnResult_Click(object sender, EventArgs e)
{
int a = 0;
int b = 0;
if (!int.TryParse(first, out a))
{
MessageBox.Show("first is not a number");
return;
}
if (!int.TryParse(second, out b))
{
MessageBox.Show("second is not a number");
return;
}
int c = a + b;
txtResult.Text = c.ToString();
}
Instead of using Convert.ToInt32(string), you might actually use Int32.tryParse(String, out int), as shown below:
int a, b;
a = Int32.tryParse(first, out a);
b = Int32.tryParse(second, out b);
If the conversion fails, the tryParse method will result in a zero. If it succeeds, it will give you the number which is to be found in the string.
Hope it helped you out, had to find this too in my first few days of C#.
Related
I am creating a Windows Form Application and I want to create a method to be able to pass in a specified text box from a _Click event. Such as below: My Method is AddTo() and I want to call from the 2 click events which have 2 separate text boxes. I want to be able to pass in the correct text box.
void AddTo(string ctrl)
{
int num= int.Parse(ctrl);
num++;
ctrl = num.ToString();
}
private void btnAddLevel_Click(object sender, EventArgs e)
{
AddTo(TextBox1.Text);
}
private void btnAddSecond_Click(object sender, EventArgs e)
{
AddTo(TextBox2.Text);
}
I am pretty new to C#, is this possible to do? Thanks in advance for any help.
UPDATE:
Here is the full code with the fix below
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
txtName.Text = "0";
}
void AddTo(ref TextBox tBox)
{
if (tBox.Text.Trim().Length > 0)
{
int num = 0;
//CHECK IF THE TEXT IS CONVERTIBLE TO NUMBER
if (int.TryParse(tBox.Text, out num))
{
num++;
tBox.Text = num.ToString();
}
}
}
private void btnAddUnit_Click(object sender, EventArgs e)
{
AddTo(ref txtName);
}
}
Use ref key word to retain data updates for passing objects.
Try below code:
//YOUR TEXTBOX IS A REFERNCE HERE. SO THAT THE UPDATES ARE RETAINED
void AddTo(ref TextBox tBox)
{
//VALIDATED YOUR TEXT BOX IF DATA EXISTS BEFORE UPDATING
if (tBox.Text.Trim().Length > 0 )
{
int num = 0;
//CHECK IF THE TEXT IS CONVERTIBLE TO NUMBER
if (int.TryParse(tBox.Text, out num))
{
num++;
tBox.Text = num.ToString();
}
}
}
While calling
//USE REF WHILE CALLING
AddTo(ref textBox1);//textbox object
I have TextBoxA and TextBoxB. What i want to do is , whenever i put a number (yes, both of the textboxes values are always integers) in TextBoxA , TextBoxB should "autocomplete" with value (100-TextBoxA). Same thing goes for TextBoxB. The sum of TextBoxA and TextBoxB should always be 100.
Here's what i've already tried:
static void TextBoxA_TextChanged()...
{
int a = Convert.ToInt32(TextBoxA.Text);
int b = Convert.ToInt32(TextBoxB.Text);
string text = (100-a).ToString();
TextBoxB.Text = text;
}
Static void TextBoxB_TextChanged()...
{
int a = Convert.ToInt32(TextBoxA.Text);
int b = Convert.ToInt32(TextBoxB.Text);
string text = (100-b).ToString();
TextBoxA.Text = text;
}
But it doesn't work.
Here's what you can try:
private void TextBoxA_TextChanged(object sender, EventArgs e)
{
int num = 0;
if (int.TryParse(TextBoxA.Text, out num))
{
string text = (100 - num).ToString();
TextBoxB.Text = text;
}
}
private void TextBoxB_TextChanged(object sender, EventArgs e)
{
int num = 0;
if (int.TryParse(TextBoxB.Text, out num))
{
string text = (100 - num).ToString();
TextBoxA.Text = text;
}
}
This will autocomplete on either TextBox on TextChanged Event.
First, i dont know why your event handlers are declared static.. its usually got to be :
private void TextBoxA_TextChanged(object sender, EventArgs e) { }
Secondly, you know if you have 2 textboxs, and each one triggers the other, you'll never go out of the TextChanged event.
To understand me more, here's an example :
1- You set TextBoxB.text = "1";2- TextBoxB.TextChanged triggers, it
sets TextBoxA.Text = "2"; 3- TextBoxA.TextChanged triggers, it sets
TextBoxB.Text = "1";
And it continues like this until i believe you'll get an Exception of memory.
EDIT : The opertator '-' works on numbers. You can't substract a number from a string. they have to be both numbers, so convert them first.
EDIT 2 :
Here's a code i wrote that works fine
private void textBox1_TextChanged(object sender, EventArgs e)
{
int n;
if (int.TryParse(textBox1.Text, out n)) // Check if the text value is a number
{
if (n > 100) // Since you want a sum of 100
return;
int m = 100 - n; // remaining
if (textBox2.Text != m.ToString()) // to not re-trigger the TextChanged event
textBox2.Text = m.ToString();
}
}
private void textBox2_TextChanged(object sender, EventArgs e)
{
int n;
if (int.TryParse(textBox2.Text, out n)) // Check if the text value is a number
{
if (n > 100) // Since you want a sum of 100
return;
int m = 100 - n; // remaining
if (textBox1.Text != m.ToString()) // to not re-trigger the TextChanged event
textBox1.Text = m.ToString();
}
}
Try this. This is a more efficient and elegant way I'd choose using lambda expressions, without repeating the method:
private void onChangeDoSum(object sender, EventArgs e,
TextBox substractNumber, TextBox sumNumber)
{
sumNumber.Text = (100 - Int32.Parse(substractNumber.Text)).ToString();
}
private void Form1_Load(object sender, EventArgs e)
{
textBox1.TextChanged += (a, b) => onChangeDoSum(sender, e, textBox1, textBox2);
textBox2.TextChanged += (a, b) => onChangeDoSum(sender, e, textBox2, textBox1);
}
Alternatively use Int32.TryParse to prevent unexpected results.
I think you can do something like this
private void textBox1_TextChanged(object sender, EventArgs e)
{
textBox2.Text = (100 - Int32.Parse(textBox1.Text)).ToString();
}
private void textBox2_TextChanged(object sender, EventArgs e)
{
textBox1.Text = (100 - Int32.Parse(textBox2.Text)).ToString();
}
when I see that static word I think you have tried to create these method by yourself and you forgot to add
textBox1.TextChanged += textBox1_Changed;
// I saw other post where you wrote that it could raise exception and fall. Of course it can. You can use if condition like
textBox1.Text != null && textBox1.Text != ""
before value would be changed or TryParse() method
i have textbox on a windows form and i want to be insert only numbers in this textbox.i use the following c# code for that
private void ChildAge_TextChanged(object sender, EventArgs e)
{
int i;
if (!int.TryParse(ChildAge.Text, out i))
{
MessageBox.Show("Plaese enter a valid Age");
}
}
it is working, but the problem is that , after showing the Message, when i Backspace the content and text box become null, on that situation also this message box shows again.
Do a little test like bellow:
int i = 0;
if(!string.IsNullOrEmpty(ChildAge.Text) &&
!int.TryParse(ChildAge.Text, out i)
)
{
MessageBox.Show("Enter Valid Age");
}
Try Using Below. This works better.
bool m_BackPressed = false;
private void ChildAge_TextChanged(object sender, EventArgs e)
{
int i;
if (!m_BackPressed)
{
if (!int.TryParse(ChildAge.Text, out i))
{
MessageBox.Show("Plaese enter a valid Age");
}
}
}
private void ChildAge_KeyPress(object sender, KeyPressEventArgs e)
{
m_BackPressed = (e.KeyChar.Equals((char)Keys.Back)) ? true : false;
}
private void txtrate_TextChanged(object sender, EventArgs e)
{
int a = Convert.ToInt32(txtqty.Text);
int b = Convert.ToInt32(txtrate.Text);
int c = a * b;
txttotal.Text = Convert.ToString(c);
//txttotal.Text = (Convert.ToInt32(txtqty.Text) * Convert.ToInt32(txtrate.Text)).ToString();
}
Well... this error occurs of txtqty.Text (or txtrate.Text for variable b) does not contain a valid number. So the user entered letters or other characters instead of 0 till 9.
You could try to validate your input first with TryParse:
private void txtrate_TextChanged(object sender, EventArgs e)
{
int a = Convert.ToInt32(txtqty.Text);
int b = Convert.ToInt32(txtrate.Text);
if (Int32.TryParse(txtqty.Text, out a) && (Int32.TryParse(txtrate.Text, out b)
{
int c = a * b;
txttotal.Text = c.ToString();
}
}
Yes, this is due to the value not contained only numbers, to avoid this situation, please setup the type of data you are trying to collect with the text fields, you can setup refer this post for a detailed walk through on how to do it.
Yes, I would suggest TryParsetoo :
private void txtrate_TextChanged(object sender, EventArgs e)
{
int number;
bool result = Int32.TryParse(txtqty.Text, out number);
if (result)
{
//Converting is Ok, proceed
}
else
{
//Convertign fail
txtqty.Focus();
MessageBox.Show("Please enter only number for this field");
return;
}
}
I would suggest making this for each textbox with setting the focus to the textbox with incorrect input and providing an useful message for the user. In my opinion this is a suitable and user-friendly way.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why am I getting a FormatException was unhandled error?
I am new to C# and Stack Overflow, so if this question is inappropriate (or in the wrong place) feel free to edit or remove it.
I've made a simple calculator, but I have a problem: when I clear one of the textboxes to enter another number a message shows saying "Unhandled exception occured" with the option to quit or continue. How can I stop this message from displaying every time I clear the texboxes?
private void button1_Click(object sender, EventArgs e)
{
int value1 = Convert.ToInt32(textBox1.Text);
int value2 = Convert.ToInt32(textBox2.Text);
textBox3.Text = sum(value1, value2).ToString();
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
int vlera1 = Convert.ToInt32(textBox1.Text);
}
private void textBox2_TextChanged(object sender, EventArgs e)
{
int vlera2 = Convert.ToInt32(textBox2.Text);
}
private void textBox3_TextChanged(object sender, EventArgs e)
{ }
int sum(int value1, int value2) {
return (value1) + (value2);
}
Use int.TryParse(string s, out int result) instead of Convert.ToInt32(string value, int fromBase)
this is happening because you are trying to convert the empty data of the TextBox to Int32.
if (int.TryParse(textBox1.Text, out vlera1))
{
//assign here
}
You'll receive a FormatException when you try to convert a string that can not be converted to a struct of type int to int. You may always use int.TryParse(string s, out int result) to see if the string is capable for int conversion before doing the conversion.
Example
private void textBox1_TextChanged(object sender, EventArgs e)
{
int x = 0; //Initialize a new int of name x and set its value to 0
if (int.TryParse(textBox1.Text, out x)) //Check if textBox1.Text is a valid int
{
int vlera1 = Convert.ToInt32(textBox1.Text); //Initialize a new int of name vlera2 and set its value to (textBox1.Text as int)
}
else
{
//DoSomething if required
}
}
private void textBox2_TextChanged(object sender, EventArgs e)
{
int x = 0; //Initialize a new int of name x and set its value to 0
if (int.TryParse(textBox2.Text, out x)) //Check if textBox2.Text is a valid int
{
int vlera2 = Convert.ToInt32(textBox2.Text); //Initialize a new int of name vlera2 and set its value to (textBox1.Text as int)
}
else
{
//DoSomething if required
}
}
Another Solution
You may always use a try-catch statement to see if an exception was thrown from the code you provide and do something if required
Example
private void textBox1_TextChanged(object sender, EventArgs e)
{
try
{
int vlera1 = Convert.ToInt32(textBox1.Text); //Initialize a new int of name vlera2 and set its value to (textBox1.Text as int)
}
catch (Exception EX)
{
MessageBox.Show(EX.Message); //(not required) Show the message from the exception in a MessageBox
}
}
private void textBox2_TextChanged(object sender, EventArgs e)
{
try
{
int vlera2 = Convert.ToInt32(textBox2.Text); //Initialize a new int of name vlera2 and set its value to (textBox1.Text as int)
}
catch (Exception EX)
{
MessageBox.Show(EX.Message); //(not required) Show the message from the exception in a MessageBox
}
}
Notice: The try-catch statement consists of a try block followed by one or more catch clauses, which specify handlers for different exceptions
Thanks,
I hope you find this helpful :)